1. Field of the Invention
The present invention relates to a method for processing a waste high-pressure fluid, which is yielded by bringing a high-pressure fluid into contact with a processing object in a high-pressure processing vessel to make unnecessary materials on the processing object accompany it.
2. Description of the Related Art
Cleaning process is indispensable for eliminating unnecessary resists after pattern forming, or etching polymers left on substrates after etching, in case photoresists are used to form patterns in a semiconductor production process.
Wet cleaning method, which comprises the steps of dipping semiconductor substrates in a stripper (a cleaning solution) to clean them, and subsequently rinsing the stripper out of the substrates with rinsing solutions such as alcohol or extra pure water, have been conventionally adopted as a cleaning method for semiconductors. Known cleaning method, for which organic or inorganic chemical compound have been used as a stripper, suffer from problems in that the stripper may not be infiltrated into the area with reentrants of detailed patterns caused by its surface tension, high viscosity, and so on. Also, it suffer from another problems in that the salient of the patterns may be destroyed caused by capillary force occurring on the interface between gas and liquid, cubical expansion on heating to dry, and so on when drying strippers and/or rinsing solutions. Accordingly, low viscosity high-pressure fluids, for example supercritical carbon dioxide fluid, are examined to be used as strippers or rinsing solutions recently.
In addition, a process for eliminating alcoholic solvents and drying substrates is required in case the substrates are dipped (to rinse) in the alcoholic solvents such as isopropanol (IPA) after developing. Low viscosity high-pressure fluids, for example supercritical carbon dioxide fluid, are proposed to be used for drying process of substrates.
The use of supercritical carbon dioxide fluid as a stripper or a rinsing solution, or the use for drying process of substrates makes the post-processing easy and safe because it vaporizes easily under atmospheric pressure. Moreover, supercritical carbon dioxide fluid can be applied at a low cost because carbon dioxide can be obtained relatively cheaply. Also, it can easily eliminate water, oils and fats etc. stuck on semiconductor substrates because of its high dissolving power and detergency almost equivalent to those of hexane. However, sole use of supercritical carbon dioxide fluid, which can hardly dissolve high polymers such as resists or etching polymers, might result in insufficient detachment and elimination. Accordingly, at least one chemical for improving detergency of supercritical carbon dioxide fluid is added, with at least one auxiliary dissolving agent (entrainer) for improving its affinity for supercritical carbon dioxide fluid. Besides, after cleaning, the surfaces of semiconductor substrates are rinsed by means of supercritical carbon dioxide fluids including auxiliary dissolving agents.
By the way, the high-pressure fluid, having been used for cleaning, rinsing and drying of substrates, which is to be drained as a waste high-pressure fluid out of a system, comprises some unnecessary materials, such as high polymers, chemicals, auxiliary dissolving agents or alcoholic solvents, all of which have been detached and eliminated in the cleaning, rinsing or drying process. Accordingly, the waste high-pressure fluid itself cannot be reused as another high-pressure fluid for cleaning of substrates.
Furthermore, it is desirable to carry out the waste high-pressure fluid processing as well as the cleaning process of substrates in a clean room because semiconductor production processes are also carried out in clean rooms. However, it is desired that the installation area of each processing unit should be as small as possible, moreover that the processing efficiency of each processing unit should be high because not only the construction but also the maintenance and the management of the clean room may costs too much.